Magnetism Important MCQ for SSC JE Electrical

 1. When a magnet is heated, it:

Options:
(i) it gains magnetism
(ii) it loses magnetism ✅
(iii) it neither loses nor gains magnetism
(iv) none of the above

Explanation: Heating a magnet increases the thermal energy of its atoms, causing misalignment of magnetic domains. As a result, the magnet loses its magnetism.

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2. Magnetic material used in permanent magnets:

Options:
(i) iron
(ii) soft steel
(iii) nickel
(iv) hardened steel ✅

Explanation: Permanent magnets require materials that retain magnetism. Hardened steel is hard and maintains alignment of domains, making it ideal for permanent magnets.

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3. Magnetic material used in temporary magnets:

Options:
(i) hardened steel
(ii) cobalt steel
(iii) soft iron ✅
(iv) tungsten steel

Explanation: Temporary magnets are easily magnetized and demagnetized. Soft iron has low retentivity and high permeability, making it suitable.

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4. Magnetic flux density is a:

Options:
(i) vector quantity ✅
(ii) scalar quantity
(iii) phasor
(iv) none of the above

Explanation: Magnetic flux density ($B$) has both magnitude and direction, hence it is a vector quantity.

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5. Relative permeability of a ferromagnetic material = 1000. Its absolute permeability will be:

Options:
(i) 10⁶ H/m
(ii) 4π × 10⁻³ H/m ✅
(iii) 4π × 10⁻¹¹ H/m
(iv) none of the above

Explanation: Absolute permeability, $\mu ={\mu }_r{\mu }_0=1000\times 4\pi \times {10}^{-7}=4\pi \times {10}^{-3}\text{H/m}$

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6. Main advantage of temporary magnets:

Options:
(i) change the magnetic flux ✅
(ii) use any magnetic material
(iii) decrease the hysteresis loss
(iv) none of the above

Explanation: Temporary magnets can easily be magnetized and demagnetized, allowing the magnetic flux to be controlled.

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7. One weber is equal to:

Options:
(i) 10⁶ lines ✅
(ii) 4π × 10⁻⁷ lines
(iii) 10¹² lines
(iv) 10⁸ lines

Explanation: 1 Weber (Wb) is equivalent to 10⁶ magnetic lines of flux.

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8. Magnetic field intensity is a:

Options:
(i) scalar quantity
(ii) vector quantity ✅
(iii) phasor
(iv) none of the above

Explanation: Magnetic field intensity ($H$) has both magnitude and direction; therefore, it is a vector quantity.

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9. Absolute permeability = 10⁻³ H/m, flux density = 1 Wb/m². Magnetising force is:

Options:
(i) 10⁻³ A/m
(ii) 4π × 10⁻³ A/m
(iii) 1000 A/m ✅
(iv) 4π × 10³ A/m

Explanation: Using $B = \mu H$,

$H=\frac{B}{\mu }=\frac{1}{{10}^{-3}}=1000\text{A/m}$

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10. Material with relative permeability slightly less than 1 is called:

Options:
(i) diamagnetic material ✅
(ii) paramagnetic material
(iii) ferromagnetic material
(iv) none of the above

Explanation: Diamagnetic materials slightly repel magnetic fields and have $\mu_r < 1$.

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11. The greater percentage of substances are:

Options:
(i) diamagnetic ✅
(ii) paramagnetic
(iii) ferromagnetic
(iv) none of the above

Explanation: Most naturally occurring materials are diamagnetic, exhibiting weak repulsion to magnetic fields.

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12. Material with relative permeability much greater than 1 is called:

Options:
(i) diamagnetic material
(ii) paramagnetic material
(iii) ferromagnetic material ✅
(iv) none of the above

Explanation: Ferromagnetic materials have high relative permeability ($\mu_r \gg 1$) and can be strongly magnetized.

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13. Magnetic flux density in air-cored coil = 10⁻² Wb/m². With a cast iron core ($\mu_r = 100$), flux density will become:

Options:
(i) 10⁻⁴ Wb/m²
(ii) 10⁴ Wb/m²
(iii) 10⁻² Wb/m²
(iv) 1 Wb/m² ✅

Explanation: Inserting a ferromagnetic core increases flux density by $\mu_r$:

$$B={\mu }_r{B}_{\text{air}}=100\times {10}^{-2}=1\text{Wb/m²}$$